Various solutions are known for decreasing the organic content of aqueous waste solutions.
A method and apparatus for water decontamination is disclosed in U.S. Pat. No. 5,630,915. According to the method an electric arc is produced between electrodes submerged into the liquid. To intensify oxidation, hydrogen peroxide is added to the waste solution in the pretreatment tank. The electrodes are connected to a capacitor that is charged by alternating current having a frequency of 60 Hz. A pulsed electric arc is thus produced between the needle-shaped anode and cathode. Due to the tapered shape of the electrodes the reaction takes place along a very small boundary surface, with the cathode losing its mass quickly; and furthermore, due to the pulsed nature of the electric arcs the method has low capacity. Therefore it can be applied cost-effectively only for treating lower quantities of waste solutions or for decreasing contamination levels thereof to a lesser degree only.
The document WO 99/01382 discloses a method and apparatus applicable for treating flowing contaminated water. According to the method an electrochemical reaction, more specifically, electrolysis is used for water treatment. The apparatus comprises an electrolytic cell comprising inlet and outlet conduits, a current source, a microprocessor control unit, an adjusting means, and a feed pump. The adjusting means is connected to feed pumps that are operated applying signals from sensors continuously measuring the pH and electric conductivity of the water under treatment. Electrodes are submerged into the fluid in the electrolytic cell, with said electrodes being connected to a DC current source with a voltage of 25 V. The applied current density is 67 A/m2. As a disadvantage of this method it should be mentioned that not all types of organic material can be decomposed with the method.
Known art treatment methods include, among others, transforming waste solutions into solid material by thermic drying as, for instance, is disclosed by German patent DE 1,639,299. A drawback of this method is its severe cost caused by the high amount of energy needed to vaporise water contained by the solution. Storing the material produced by the process in an environmentally friendly way is costly and involves further difficulties.
Another known art method is the decomposition of organic material using ozone. As disclosed by U.S. Pat. No. 4,761,208, the method involves introducing hydrogen peroxide into the waste solution containing organic materials. The efficiency of the method is, however, rather poor, and, because residual organic radicals cannot be got rid of—not even when the efficiency of ozone decomposition is ameliorated by means of a catalyst—, decomposition is incomplete. An additional drawback of the method is that it is difficult to control.
A further solution for decreasing of organic content from aqueous solutions is biological decomposition. Using this method, however, the EDTA content of the solution cannot be removed, and furthermore, the bactericidity of the solution cannot be reduced.